Thanks for the feedback. I tried to design the wallet to be easy to use and understandable for everyone. Some aspects are non-trivial and it's hard to explain what's going on if the user has no technical knowledge about the keys, hierarchy, etc. I will try to rewrite it to be a bit more user-friendly.

To answer your specific questions:

1. If you replace the active and posting keys then yes, you won't be able to use anything else than hiveledger.io online wallet (because it's the only wallet that supports ledger devices for now). If you want your account to be protected, I recommend replacing the owner key, leaving active and posting untouched.

2. I will rewrite it to that will replace your owner key. The onboarding process is quite simple, it's just matter of replacing your old keys with those derived from the ledger device. Due to technical solutions, an online wallet needs to generate a new set of keys on your device and check if they are not used anywhere else. When it finds an appropriate candidate, you will be asked to confirm the key and it will replace your current owner key. The same applies to other roles as well.

3. That's hard to explain everything on the wallet because we have limited space there and I believe people should get familiar with keys yet before they decide to play with it. But as I already said - ledger keeps your private keys. Online wallet generates a new set and replaces your current keys with those from the device.

The best way to start is to use the FAKENET version available at https://fakenet.hiveledger.io. This way you will be able to play around, check how it's working and you won't interact with the mainnet. On fakenet, your assets are useless and have no value.